Air source heat pumps have become a formidable rival for geothermal heat pumps following the introduction of new variable speed compressor technology, which radically expands the range of temperatures at which they can effectively operate.
Last year, key manufacturers such as Waterfurnace Renewable Energy and LSB Industry subsidiary Climate Master managed to achieve major breakthroughs in efficiency via the incorporation of variable speed compressors into their heat pump systems.
While the new technology can be incorporated into both geothermal heat pumps and air source heat pumps, it promises to confer greater benefits upon the latter, which has long been viewed as the lesser of the pair due to its climate limitations.
Both geothermal heat pumps and air source heat pumps operate according to the same basic principle - they employ a refrigeration cycle to introduce external heat to an indoor environment during cold weather conditions while conversely expelling heat from buildings to cool them during hot weather.
Where they differ is in the site of their exchange mechanisms. Geothermal heat pumps transfer heat to or from the ground via large tubes which are buried beneath the earth, while air source heat pumps exchange heat with the outside atmosphere via mechanisms akin to those employed by home air conditioners.
Geothermal pumps have long been considered superior to air source pumps on account of their ability to operate in just about any climate conditions by taking advantage of constant ground temperatures. Air source pumps, on the other hand, have traditionally been far less capable of functioning effectively in colder climates as their heating performance dwindles swiftly below temperatures of only five degrees Celsius.
Variable speed technology promises to remedy this shortcoming and radically expand the range of temperatures at which air source pumps are capable of functioning efficiently. The introduction of variable speed technology means air source pumps can now operate at temperatures as low as minus-17 degrees Celsius, making them a viable alternative for all but the most extreme weather conditions.
While air source pumps are still less efficient than geothermal pumps at the upper end of the scale, they possess the key advantage of easier and cheaper installation as they do not require the burial of large-scale tubes beneath the ground.
A shift toward air source heat pumps may have already begun in North America, where Marc Rosenbaum, the director of engineering for South Mountain Company on Martha's Vineyard in Massachusetts, reports that almost all the buildings he has worked on recently have opted for the devices.
According to Tom Konrad of Forbes Magazine, while geothermal heat pumps are set to remain the more efficient alternative, air source heat pumps could become preferable in areas with mild climates, or the market sector covering retrofits and well-insulated small buildings.